Electric motors for small-scale electrical appliances have been described in a wide variety of embodiments. For example, Patent No. DE 1 151 307 A discloses an oscillating armature drive for dry shaving apparatus, which has a shaving cutter with a reciprocating working motion, and which has a U-shaped electromagnet formed fast with the housing of the shaving apparatus. A working armature and a compensating armature, on either side of the working armature, are arranged for oscillation in close proximity to the poles of the electromagnet. In the operating mode, the working armature, which drives a shaving cutter, oscillates in parallel with the pole faces of the electromagnet, and the compensating armatures perform an oscillatory motion in phase opposition thereto in order to prevent, as far as possible, the oscillations of the working armature being transferred onto the housing of the shaving apparatus.
U.S. Pat. No. 5,632,087 further discloses a dry shaver with a linear motor. The linear motor has a stator coil and several rotors equipped with permanent magnets, which are excited into a state of linear oscillation by the stator coil. The displacements of the rotors are detected by means of detectors associated with the rotors, and are further processed in the form of an average value. In the process, the supply of current to the stator coil is controlled as a function of the average value, in such a way that the oscillation amplitudes of all rotors are maintained as constant as possible. The detectors each have one permanent magnet, which is positioned on the respective rotor, and one positionally fixed sensor coil in which an induction voltage dependent on the velocity of the respective rotor is generated as a result of the effect of the permanent magnet.
Patent No. EP 1 193 844 A1 discloses a linear oscillator in which a housing constructed as a stator accommodates a rotor that executes a reciprocating motion. Also movably arranged in the housing is a spindle for controlling the oscillation amplitude of the rotor. The rotor and the spindle are coupled to each other, and to the housing, by means of springs. The coupling of the rotor with the housing can be performed by means of a helical spring having its one end secured to the housing and its other end secured to the rotor. In this arrangement, the spring not only exerts a force in axial direction during compression and extension, but also slightly rotates the rotor each time, so that an oscillatory rotational motion is generated, in particular if the excitation takes place with the resonant frequency of the oscillatory rotational motion.
With these arrangements, initially only linear oscillation is generated. In Patent No. EP 1 193 844 A1, there is disclosed the possibility of additionally generating an oscillatory rotational motion from the oscillatory linear motion by means of a spring. However, the oscillatory rotational motion generated in this way is coupled to the oscillatory linear motion and necessarily requires excitation of the oscillatory linear motion. Furthermore, the oscillatory rotational motion invariably has the same frequency as the oscillatory linear motion, so that the variation possibilities are very limited.